1. Field of the Invention
The present invention relates to an insert rotary cutter having at least one indexable cutter insert of a positive type attached to a periphery of a cutter body thereof so as to have a positive rake in the axial direction.
2. Prior Art
Recently, an indexable cutter insert, particularly the type which comprises a quadrilateral plate including a pair of side faces serving as rake surfaces for main cutting edges, has been developed, and an insert rotary cutter having such cutter inserts has been employed as an end milling cutter, a side milling cutter, a face milling cutter or the like. One such cutter insert and several rotary cutters incorporating the same are shown in FIGS. 1 to 17 of the accompanying drawings in which the same or similar members are designated by the same reference characters.
One cutter insert 100 shown in FIGS. 1 to 3 comprises a generally parallelogrammic plate defined by a front face 102, a rear face 104 disposed generally parallel to the front face 102, and four side faces 106. The insert 100 has a pair of main cutting edges 108 defined by the front face 102 and a pair of the opposite side faces 106, and the pair of side faces 106 serve as rake surfaces 110 for the main cutting edges 108, respectively. The rake surfaces 110 are flat and sloping inwardly in a direction away from the front face 102, and the width of the insert 100 between the rake surfaces 110 is uniform along the entire length of each main cutting edge 108 from its foremost end 108a to its rearmost end 108b. Those corner portions of the insert 100 defined by the front face 102 and the other pair of opposite side faces 106 are rounded off to provide rounded portions 112, and two diagonally-disposed corner portions of the insert 100 each defined by two side faces 106 intersecting at an acute angle have respective forward portions disposed adjacent to the main cutting edges 108 and serving as corner cutting edges 114, respectively, the corner cutting edges 114 being associated with the main cutting edges 108, respectively. Those portions of the other pair of opposite side faces 106 disposed adjacent to the corner cutting edges 114 serve as relief surfaces 116 for the corner cutting edges 114, respectively. The insert 100 also includes a central mounting hole 118 formed therethrough.
An example of a cutter employing the insert 100 described above is shown in FIGS. 4 to 7. The cutter, indicated generally at 120, comprises a generally cylindrical cutter body 122 adapted to be fixedly secured to a machine spindle so that the cutter body 122 can be rotated about an axis X therethrough. Formed in a circumferential surface of the cutter body 122 at its forward end are a pocket 124 and an insert receiving recess 126, the recess 126 being adjacent to the pocket 124 and opening thereto. The insert 100 is received in the recess 126 with the rear face 104 resting on a bottom thereof, and releasably fixed thereto through a clamp screw 128 extending through the mounting hole 118 and threaded into the bottom of the recess 126. Thus, one of the main cutting edges 108 and the corner cutting edge 114 adjacent thereto are indexed in their respective cutting positions so that the indexed main cutting edge 108 is presented radially outwardly of the cutter body 122 while the indexed corner cutting edge 114 is presented axially in advance of the cutter body 122. The disposition of the insert 100 is such that the rake surface 110 for the indexed main cutting edge 108 has, as shown in FIG. 5, a positive rake angle A in the axial direction, which angle A corresponds to a mounting inclination angle of the insert 100 with respect to the cutter body 122, and that when the cutter body 122 is rotated about its axis X, the foremost and rearmost ends 108a and 108b of the indexed main cutting edge 108 generate respective circles 130 of an equal diameter disposed coaxially with the cutter body 122.
Another conventional rotary cutter 120a shown in FIGS. 9 to 12 differs from the aforementioned cutter 120 in that a cutter body 122a has a plurality of, say four, pockets 124a formed in the circumferential surface of its forward end in circumferentially and axially equally spaced relation to one another. The cutter body 122a also has a plurality of recesses 126a formed in its circumferential surface, each recess 126a being adjacent to a respective one of the pockets 124a and opening thereto. The same inserts 100 as that described above are releasably mounted in the recesses 126a, respectively, in such a manner that the inserts 100 are disposed in overlapping relation, as shown in FIG. 9, when the cutter body 122a is viewed in the circumferential direction. One of the main cutting edges 108 of each insert 100 is indexed in its peripheral cutting position so as to be presented radially outwardly of the cutter body 122a, and one of the corner cutting edges 114 of the insert 100 closest to a forward end face of the cutter body 122a is indexed in its face cutting position so as to be presented axially in advance of the cutter body 122a. The rake surface 110 for the indexed main cutting edge 108 of each insert 100 has a positive rake angle A in the axial direction, as shown in FIG. 11, and the foremost and rearmost ends 108a and 108b of each indexed main cutting edge 108 generate respective circles 130a of an equal diameter disposed coaxially with the cutter body 122a, as shown in FIG. 12, when the cutter body 122a is rotated.
Still another conventional rotary cutter 120b shown in FIGS. 14 to 17 comprises a disk-shaped cutter body 122b defined by a forward axial face 140, a rearward axial face 142 and a circumferential surface 144. The cutter body 122b includes a plurality of pockets 124b formed in its circumferential surface 144 in circumferentially spaced relation to each other. Also formed in the circumferential surface 144 of the cutter body 122b are two groups of recesses 126b and 126c disposed in staggered relation so that one group of recesses 126b open to the forward axial face 140 while the other group of recesses 126c open to the rearward axial face 142, each of the recesses 126b and 126c being also disposed adjacent to a respective one of the pockets 124b and opening thereto. Releasably mounted in each of the recesses 126b and 126b is the same insert as that described above, the inserts in the recesses 126b being designated at 100a while the inserts in the recesses 126c are designated at 100b. The insert 100a and the insert 100b are inclined in opposite circumferential directions with respect to the cutter body 122b, and one of the main cutting edges 108 of each insert 100a, 100b and the corner cutting edge 114 adjacent thereto are indexed in their respective working positions so that the rake surface 110 for the indexed main cutting edge 108 has a positive rake angle A in the axial direction. As shown in FIG. 16, the indexed main cutting edges 108 of the inserts 100a and 100b are disposed in overlapping relation when the cutter body 122b is viewed in the circumferential direction, and the foremost and rearmost ends 108a and 108b of the indexed main cutting edges 108 generate respective circles of an equal diameter disposed coaxially with the cutter body 122b when the cutter body 122b is rotated about its axis X.
In the prior art cutters 120, 120a and 120b described above, when desired to obtain better cutting performance, it is necessary to use the insert 100 designed so as to have a sufficiently large axial rake angle A. However, since the insert 100 has to be disposed so as to have an appropriate relief angle B for the indexed corner cutting edge 114, in order for the insert 100 to have the large rake angle A, the corner angle C of the indexed corner cutting edge 114 has to be made acute excessively. As a result, the strength of the insert 100 at its indexed corner cutting edge 114 is lowered, and it is likely to lead to the damage of the insert 100 in use. Furthermore, in addition to being straight, the indexed main cutting edge 108 of the insert 100 is sloping circumferentially of the cutter body 122, 122a, 122b since the insert 100 is disposed so as to have a positive rake angle A in the axial direction. Accordingly, when the cutter body 122, 122a, 122b is rotated about its axis X during cutting operation, the indexed main cutting edge 108 of the insert 100 generates a modified cylinder, the diameter of the cylinder being smaller at the intermediate portion intermediate the opposite ends thereof than of the opposite ends which are generated by the foremost and rearmost ends 108a and 108b of the main cutting edge 108. Therefore, when a workpiece W is machined with the cutter 120, 120a, 120b described above, the machined surface S has a convex shape, as illustrated in FIG. 8, or an undulatory shape, as illustrated in FIG. 13, so that the machining precision and surface finish are unsatisfactory. In addition, in the cutter 120 a, 120b having a plurality of cutter inserts 100, the overall cutting resistance of the cutter is larger, and besides it is difficult to obtain sufficient rigidity due to the structure having a plurality of pockets 124a, 124b, so that the cutter body 122a, 122b is liable to chattering and vibration when in use.